Herein disclosed are imaging members useful in electrostatographic apparatuses, including printers, copiers, other reproductive devices, and digital apparatuses. Some specific embodiments are directed to imaging members that have nano-size particles serving as fillers dispersed or contained in one or more layers of the imaging member. The nano-size particles provide, in some embodiments, an imaging member with a transparent, smooth, and less friction-prone surface. In addition, the nano-size particles may provide a imaging member with longer life and reduced marring, scratching, abrasion and wearing of the surface. Furthermore, the nanoparticle filler has good dispersion quality in the selected binder and reduced particle porosity. Thus, incorporation of the nano-size particles into the imaging member provides for increased mechanical strength and improved wear.
In electrostatographic reproducing apparatuses, including digital, image on image, and contact electrostatic printing apparatuses, a light image of an original to be copied is typically recorded in the form of an electrostatic latent image upon a imaging member and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles and pigment particles, or toner. Electrophotographic imaging members may include imaging members (photoreceptors) which are commonly utilized in electrophotographic (xerographic) processes, in either a flexible belt or a rigid drum configuration. Other members may include flexible intermediate transfer belts that are seamless or seamed, and usually formed by cutting a rectangular sheet from a web, overlapping opposite ends, and welding the overlapped ends together to form a welded seam. These electrophotographic imaging members comprise a photoconductive layer comprising a single layer or composite layers.
The term “electrostatographic” is generally used interchangeably with the term “electrophotographic.” In addition, the terms “charge blocking layer” and “blocking layer” are generally used interchangeably with the phrase “undercoat layer.”
One type of composite photoconductive layer used in xerography is illustrated in U.S. Pat. No. 4,265,990 which describes a imaging member having at least two electrically operative layers. One layer comprises a photoconductive layer which is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer (CTL). Generally, where the two electrically operative layers are supported on a conductive layer, the photoconductive layer is sandwiched between a contiguous CTL and the supporting conductive layer. Alternatively, the CTL may be sandwiched between the supporting electrode and a photoconductive layer. Imaging members having at least two electrically operative layers, as disclosed above, provide excellent electrostatic latent images when charged in the dark with a uniform negative electrostatic charge, exposed to a light image and thereafter developed with finely divided electroscopic marking particles. The resulting toner image is usually transferred to a suitable receiving member such as paper or to an intermediate transfer member which thereafter transfers the image to a member such as paper.
In the case where the charge-generating layer (CGL) is sandwiched between the CTL and the electrically conducting layer, the outer surface of the CTL is charged negatively and the conductive layer is charged positively. The CGL then should be capable of generating electron hole pair when exposed image wise and inject only the holes through the CTL. In the alternate case when the CTL is sandwiched between the CGL and the conductive layer, the outer surface of CGL layer is charged positively while conductive layer is charged negatively and the holes are injected through from the CGL to the CTL. The CTL should be able to transport the holes with as little trapping of charge as possible. In flexible web like imaging member the charge conductive layer may be a thin coating of metal on a thin layer of thermoplastic resin.
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, however, degradation of image quality was encountered during extended cycling. The complex, highly sophisticated duplicating and printing systems operating at very high speeds have placed stringent requirements including narrow operating limits on imaging members. For example, the numerous layers used in many modern photoconductive imaging members must be highly flexible, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. One type of multilayered imaging member that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, an optional blocking layer, an optional adhesive layer, a CGL, a CTL and a conductive ground strip layer adjacent to one edge of the imaging layers, and an optional overcoat layer disposed on the CTL. Such an imaging member may further comprise an anti-curl back coating layer on the side of the substrate opposite the side carrying the conductive layer, support layer, blocking layer, adhesive layer, CGL, CTL and other layers.
In a typical machine design, a flexible imaging member belt is mounted over and around a belt support module comprising numbers of belt support rollers, such that the top outermost charge transport layer is exposed to all electrophotographic imaging subsystems interactions. Under a normal machine imaging function condition, the top exposed charge transport layer surface of the flexible imaging member belt is constantly subjected to physical/mechanical/electrical/chemical species actions against the mechanical sliding actions of cleaning blade and cleaning brush, electrical charging devices, corona effluents exposure, developer components, image formation toner particles, hard carrier particles, receiving paper, and the like during dynamic belt cyclic motion. These machine subsystem interactions against the surface of the charge transport layer have been found to consequently cause surface contamination, scratching, abrasion—all of which can lead to rapid charge transport layer surface wear problems. Thus, a major factor limiting imaging member life in copiers and printers, is wear and how wear affects the multiple layers of the imaging member. For example, the durability of the charge transport and overcoat layers, and the ability of these layers to resist wear will greatly impact the imaging member life.
Many current imaging members have their top charge transport layers comprised of dispersed charge transport molecules or components in polycarbonate binders. The charge transport molecule or component may be, for example, represented by the following structure:
wherein X is selected from the group consisting of alkyl, alkoxy, and halogen. In embodiments the alkyl and alkoxy contain from about 1 to about 12 carbon atoms. In other embodiments, the alkyl contains from about 1 to about 5 carbon atoms. In yet another embodiment, the alkyl is methyl. In an embodiment, the charge transport molecule is (N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl-)-4,4′diamine).
In order to provide a sufficient charge transporting capability, the charge transport molecule loading level is typically very high, for example, around 43 percent to 50 percent by weight of the total weight of the charge transport layer. High charge transport molecule content leads to poor physical properties of the device, for example, a decrease in mechanical strength. Moreover, charge transport compound m-TBD content constitutes one of the most expensive components of the imaging member. Consequently, high charge transport molecule content increases the cost of imaging member devices. Thus, maintaining sufficient charge transporting capability in current imaging members not only increases the associated costs but also decreases the mechanical strength of the imaging member.
The overcoat layer provides an outer level of protection on the imaging member and may help bolster wear resistance and scratch resistance of the charge transport layer in the print engine. Because the overcoat layer is one of the outermost layers of the imaging member, it is subjected to more wear and friction than some of the other layers. Thus, how well the overcoat layer is maintained will greatly affect imaging member life.
Another limiting factor is associated with the anti-curl back coating layer. In the production of multilayered imaging members, the drying/cooling process used to form the layers will often cause upward curling of the multiple layers. This upward curling is a consequence of thermal contraction mismatch between the CTL and the substrate support. Curling of a imaging member web is undesirable because it hinders fabrication of the web into cut sheets and subsequent welding into a belt. To offset the curling, an anti-curl back coating is applied to the backside of the flexible substrate support, opposite to the side having the charge transport layer, to render the imaging member web stock with desired flatness. Common anti-curl back coating formulations, however, do not always providing satisfying dynamic imaging member belt performance result under a normal machine functioning condition; for example, exhibition of anti-curl back coating wear and its propensity to cause electrostatic charging-up are the frequently seen problems to prematurely cut short the service life of a belt which requires frequent and costly replacements. The electrostatic charge build up is due to contact friction between the anti-curl layer and the backer bars, which increases the friction and thus requires higher torque to pull the belts. Because the anti-curl back coating is an outermost exposed layer and has high surface contact friction when it slides over the machine subsystems of belt support module, such as rollers, stationary belt guiding components, and backer bars, during dynamic belt cyclic function, these mechanical sliding interactions against the belt support module components not only exacerbate anti-curl back coating wear, but also cause the relatively rapid wearing away of the anti-curl layer which produces debris. Such debris scatters and deposits on critical machine components such as lenses, corona charging devices and the like, thereby adversely affecting machine performance. Thus, how well the overcoat layer is maintained will greatly affect imaging member life.
Therefore, there is a need for an alternative design of the imaging member in which mechanical wear can be reduced while improving the electrical properties in the various layers, such as the overcoat layer, anti-curl back coating layer and charge transport layer, without high costs.